This invention relates to the detection of switch closure in an array of switches and, more particularly, to an arrangement for minimizing the number of connections needed between an array of switches and the circuit used to detect and encode switch closure.
Input switch arrangements for keyboards are conventionally constructed of a substantially rectangular array of switches formed into a matrix where the product of the number of rows and the number of columns is the total number of switches in the matrix and the sum of the number of rows and the number of columns is the number of connections needed. A single switch element is provided at the intersection of each column and each row which, when operated, connects the respective column with the respective row. Switch closure is conventionally detected by putting a known voltage on a column (or row) and then sequentially examining each row (or column) to determine if there is a connection. This is repeated for all the columns (or rows) in the matrix.
While effective, the aforedescribed arrangement is disadvantageous because, for example, a relatively large number of connections are required (the sum of the number of columns and the number of rows) and a relatively long scan time is needed, especially for a large matrix. The first of these disadvantages is particularly acute when utilizing integrated circuits because of the limited number of terminals available on an integrated circuit chip.
It is therefore an object of this invention to provide an input switch arrangement which overcomes the above stated disadvantages.
It is a further object of this invention to provide an input switch arrangement which minimizes the number of connections required between the input switches and the switch closure detection and encoding circuitry.
It is another object of this invention to provide an input switch arrangement which minimizes the amount of time required for detecting the identity of the closed switch in an array of switches.